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Tornado, Rockwell Pass
Sequoia National Park, July 7, 2004
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Highest Elevation Tornado Ever Observed in U.S.
Analyses and Documentation:
John Monteverdi, SFSU
Roger Edwards, SPC
Greg Stumpf, NSSL
Daniel Gudgel, NWS San Joaquin Valley Weather Forecast Offce
Email: montever@sfsu.edu
Tornado Pictures, All Rights Reserved, Scott Newton, 2004
(Permission to use pictures granted. Please give attribution to Scott Newton)
Thunderstorm Picture, All Rights Reserved, Bill Hensley, 2004
(Permission to use picture granted. Please give attribution to Bill Hensley)
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Tornado Pictures / Hail Picture / Thunderstorm Picture/ Location Maps / Account of Storm / Meteorological Analysis
4:32 PM PDT 7 July 2004: View to the Southwest
While on a backpacking trip into the eastern portion of Sequoia National Park, Scott Newton encountered a tornadic thunderstorm. White streaks are falling hail stones.
4:37 PM PDT 7 July 2004: View to the Southwest
Elevation at Rockwell Pass: ~11,600 feet. Base of tornado at ground level probably at least at 12,000 feet. This makes this tornado the highest elevation tornado ever observed in the U.S.
Scott estimates that the hail size, verified by this picture, was between 3/4" and 1".
Hail-fall lasted one hour.
This shot was taken on 07 July between Lone Pine and Keeler, CA, at 4:17PM Pacific, looking to the northwest. Note the backsheared anvil and overshooting top. Picture by Bill Hensley.
USGS topographic maps showing location of Rockwell Pass, the Rattlesnake RAWS site and the Kern River Canyon, as explained in the text.
Map of south-central California, showing locations of Rockwell Pass, KHNX, KVBG and KEYX, as discussed in the text.
At 2337 UTC (4:37 PM PDT) July 7, 2004, a backpacker in the Rockwell Pass area of Sequoia National Park (west of Mt. Williamson in the southern Sierra Nevada) photographed a tornado (Fig. 1). The tornado had developed northwest of Rockwell Pass over the upper sections of the steeply-walled Kern River Canyon (Fig. 2). Since the elevation of Rockwell Pass is approximately 3500 m (~11600 ft), we believe this to be the highest elevation tornado photographed and documented in the United States. Observers estimated that hail exceeding severe limits accompanied the storm and covered the ground in places. The former observation is corroborated by photographs of the hail (Fig. 3).
The tornado circulation quickly propagated to ground level. Later photographs show considerable debris entrained into the condensation funnel. In several of the photographs the fall of large hail is evident.
Photographs of the developing thunderstorm from about 30 km to the southeast (Fig. 5) show a number of interesting features. These include a well developed and crisp anvil with backshear, and the suggestion of an overshooting top, which would have been centered over the headwaters of the Kern River Canyon.
Although tornadoes are not rare in California (as discussed in Monteverdi et al. (2003) and many other studies), documentation on tornadoes in the mountainous areas of California (or in any state) is sparse. By coincidence, a tornado that occurred in the same general geographic area was observed and documented in the late 1970s (Bluestein 1979). The most famous and well-documented high mountain supercell tornado was the F4-rated Yellowstone/Teton Wilderness tornado of 1987 (Fujita 1989). Interestingly, this tornado and parent thunderstorm formed in an area with topography as rugged as that in the southern Sierra Nevada, although elevations in the Rockwell Pass area are much higher.
The purpose of this paper is to present a brief examination of the synoptic and thermodynamic controls of this event. Since the photographic documentation presented above suggested to the authors that the parent storm may have been a supercell, we took special care in establishing the shear setting, to the degree it was possible, and examining the available radar information.
